1. Field of the Invention
The present invention relates to an indexable cutter insert having a cutting edge and a cutting face provided with protrusions for breaking cuttings produced by the cutting edge into chips.
2. Prior Art
As indexable cutting inserts (hereinafter referred to simply as "tips") of this kind, for example, there is known a tip as illustrated in FIG. 1. This tip 1 is disclosed in Japanese Utility Model Application, Laid-Open Number 61-151806. The tip 1 comprises a plate-like insert body 2 in the shape of a polygon (in this example a parallelogram) shown in a plan view. A cutting face 3 is formed on a front face of the insert body 2, and cutting edges 6 having a nose portion 5 at the corner of the above-mentioned polygon are formed at the intersection of the cutting face 3 and a flank face 4 formed on the peripheral face of the insert body 2.
The cutting face 3 is connected as shown in FIG. 2 to a cutting edge 6 via a land portion 7, and is formed with an inclined face which is downsloped toward the center portion of the above-mentioned front face. The inclined angle .alpha..sub.0 of the inclined face is equal to the rake angle of the cutting edge 6. Furthermore, on the front face, a plane face perpendicular to a line extending in the direction of the thickness of the insert body 2 is formed. The plane face is used for a chip breaker face 8 which projects outwardly in the direction of the thickness of the insert body 2 with respect to the extended plane stemming from the cutting face 3. Furthermore, the cutting face 3 formed in an inclined face, and the chip breaker face 8, are smoothly connected to each other by a curved face 9 with a large radius of curvature.
Similarly, on the curved face 9 and cutting faces 3, as shown in FIGS. 1 and 3, protrusions 10 are formed a certain distance away from the cutting edge 6. The protrusion 10 is in the shape of a hemisphere projecting outwardly from the cutting face 3 and curved face 9, in the direction of the insert thickness. In this example, a plurality of these types of protrusions 10 are arranged along the direction of the cutting edge 6. Additionally, in this example, protrusions 11 are formed at a location further from the projections 10 away from the cutting edge 6. The protrusion 11 are in the shape of a hemisphere larger than the projection 10, and outwardly project from the chip breaker face 8 in the direction of the insert thickness. Furthermore, in FIG. 1, numeral 12 indicates an installation aperture used for installing the insert 1 to a tool such as a cutting tool.
On the other hand, there is known another tip 13 as illustrated in FIGS. 4 and 5. The tip 13 comprises a cutting face 3 which concaves inwardly towards the thickness of insert body 2, and a chip breaker face 8 which projects outwardly in the direction of the insert thickness with respect to the extended plane stemming from the cutting face 3.
The cutting face 3 and the chip breaker face 8 are smoothly connected by the curved face 9 with a large radius of curvature, as in the case of the above-mentioned tip 1. Moreover, on the cutting face 3, chip breaker face 8 and curved face 9, protrusions 14 are formed as illustrated in FIG. 6 showing a cross section.
The protrusion 14, as shown in FIG. 6, is formed in a so-called tear-drop shape. That is, an end portion 16 of the protrusion 14, which is disposed near the cutting edge 6, is generally a half-conical shape. In contrast, opposite end portion 17 of the protrusion 14 is generally a quarter-spherical shape, and is smoothly connected to the end portion 16. In the insert 13 shown in FIGS. 4 through 6, identical numerals were used to indicate corresponding portions with the insert shown in FIGS. 1 through 3, thus this explanation will be omitted.
The purpose of these protrusions 10, 11, and 14 provided in inserts 1 and 13 is to break cuttings produced by the cutting edge 6 into small chips during a cutting operation. That is, in the inserts 1 and 13 provided with protrusions 10, 11, or 14, cuttings shaved off from the workpiece elongate contacting with the curved face 9; pass over protrusions 10, 11, or 14; and are forced curl so as to be broken into small chips.
In the tips 1 and 13, by means of the outwardly curved surface shape or tear-drop shape of the protrusions 10, 11, and 14, a V-shaped concave portion 18 is formed between the cutting edge 3 and the protrusions. For this construction, cuttings shaved off by cutting edge 6 pass over the concave portion 18 and pass over protrusions 10, 11 and 14; in this way, the curl diameter of the cuttings is reduced, and due to this, breaking of the cuttings can be more effectively accomplished.
In the cutting process using this type of insert, when the cutting depth and the cutting feed rate are small, the thickness of cuttings formed during this so-called light cutting operation become relatively small. In contrast, during heavy cutting operations, in the case when the cutting depth and the cutting feed rate are fairly large, cuttings with a relatively large thickness are formed.
However, in the case when the cuttings with this type of relatively large thickness are formed, in the inserts 1, 13 possessing outwardly curved protrusions 10 and 11 or tear-drop shaped protrusions 14, as mentioned above, these successively formed cuttings are forced to curl at the V-shaped concave portion 18, so that a small curl diameter is rapidly formed. As a result, large resistance is exerted on the tip 1. Moreover, the curled cuttings is brought into continual contact with the cutting face of the workpiece before being broken, so that the smooth discharge of chips is disrupted and the chips become clogged and accumulated at the cutting position.
When these chips clog and are accumulated, the cutting resistance becomes large and cutting accuracy is deteriorated. Additionally, there is a danger of breaking of the cutting edge by a large load exerted thereon.
In order to solve the above-mentioned problems, there is proposed the formation of the protrusion 10 with a small height to curl the cuttings T.sub.1 of large thickness in a large diameter, as shown by the dotted line in FIG. 7.
However, in the case when the feed rate is low, and the thickness of the cuttings T.sub.2 is small, as shown by the solid line in FIG. 7, the cuttings cannot be sufficiently curled. Consequently the cuttings are discharged in the form of a continuous ribbon. As a result, the ribbon of the cuttings comes into contact with the cutting face of the workpiece W and cutting accuracy is deteriorated; the cuttings also become coiled around the tool and the workpiece W, which prevents a smooth cutting operation.
Additionally, even after the cuttings are curled, it is difficult to rapidly break them into chips. Therefore, the shapes of the cuttings generated by this continuous generation can be classified into several different categories, depending on the cutting conditions such as the feed rate and the cutting depth, as well as the shape and the size of a tip. That is, cuttings are produced in the shape of a straight ribbon running along the cutting face almost without being curled in the a shaved off condition caused by the cutting edge. Moreover, there are also the cases when a coiled shape (running along the cutting face), a cylindrical shape (set away from the cutting face or the cutting edge), or a conical shape, are drawn and set slanting in relation to the cutting edge and the cutting face.
However, as mentioned above, in the case when the straight ribbon (running along the cutting face) or coiled shapes are created, two types of problems occur: when the aforementioned type of cuttings come into contact with the cutting face, the cutting accuracy is deteriorated; and when the above generated cuttings are accumulated in between the tip and the workpiece to be cut, there arises to a large increase in cutting resistance.
In order to avoid the occurrence of these types of problems, it is possible to create the cuttings in a direction set apart from the cutting face of the material to be cut. However, in the tip of the above mentioned example, due to the outwardly-curved projections, there is the possibility that the cuttings, which are in contact with the aforementioned outwardly-curved surface, may be discharged in any direction. Thus, it is extremely difficult to control the direction in which the cuttings will be generated.